Interpretive Summary: Potato is grown in mixed cropping systems in the highlands of Cameroon. The perennial occurrence of late blight is a significant constraint to potato production. Identification of additional hosts is important in understanding potential sources of inoculum for late blight. To identify alternative hosts for P. infestans occurring in multiple-cropping systems, laboratory and greenhouse studies were conducted. Twelve solanaceous and fourteen asteraceous species were inoculated with late blight isolates obtained from garden huckleburry, potato and tomato. The infection of gboma eggplant(Solanum macrocarpon),billy goatweed (Agaratum conyzoides) and Worowo(Solanum biafrae)and the detection of late blight on Solanum scabrum (garden huckleburry) and other hosts suggests that they are alternative hosts and involved in the perpetuation of late blight in the potato agro-ecosystem in Cameroon. Destruction or removal of alternate hosts can readily reduce late blight inoculum and be used for late blight management by potato growers.

Technical Abstract:
Experiments were conducted to detect potential hosts of Phytophthora infestans, causal agent of potato late blight among weeds occurring in Cameroon. Isolates of P. infestans isolated from garden huckleberry (Solanum scabrum), potato (S. tuberosum) and tomato (Lycopersicon esculentum) were inoculated on detached leaves of 12 solanaceous and 14 asteraceous species collected from the potato agro-ecosystem in the western highlands of Cameroon. Isolates of P. infestans from huckleberry, potato and tomato infected the same host plants. Isolates from huckleberry and potato infected gboma eggplant (Solanum macrocarpon) and two asteraceous weeds, Ageratum conyzoides (Billy goatweed) and Dichrocephala integrifolia (Dichrocephala). P. infestans isolate from Potato infected Aspilia africana (haemorrhage plant) and a tomato isolate infected Solanecio biafrae (Worowo). Inoculum obtained from infected S. macrocarpon caused late blight symptoms on huckleberry, potato and tomato both under laboratory and screen house conditions. Inoculum from the two species of asteraceous weeds infected potato, and inoculum from Solanecio biafrae infected huckleberry in laboratory and screen house studies. This is the first report of late blight infection on Solanum macrocarpon, Ageratum conyzoides, Aspilia africana, Dichrocephala integrifolia and Solanecio biafrae in Cameroon. Results indicate that these asteraceous and solanaceous weeds are potential alternative hosts for P. infestans in the potato agro-ecosystem in Cameroon.